It is known that, when a short pulse laser is focused on an inside a transparent medium such as quartz glass, a minute deformed region is formed, in which the refractive index is different from that of surroundings thereof. Forming a plurality of such minute deformed regions inside the medium in three-dimensions and using it for recording information, has been studied.
In Patent Literature 1 and 2, and Non-patent Literature 1 described below, a three-dimensional memory is disclosed, in which a recording mark of which the refractive index is different from that of the surrounding glass is formed locally on a glass. The mechanism in which the local deformation is formed by a short pulse laser is disclosed in Non-patent Literature 2, for example.